The present invention relates to a device providing a signal indicating the rotational position of a rotary shaft. The device is particularly suitable for application in adverse environmental conditions, such as corrosive and/or explosive chemical environments. The application of the present invention specifically relates to fluid and other flow systems in which it is considered desirable t monitor the condition of rotary valves (i.e. open or closed) and/or to control the opening or closing of successive valves in the flow lines as a function of the state of preceding valves. The prior art included electrical switches that are mechanically activated in response to this operative state of the rotary valve. Such mechanically activated switches were frequently subjected to severe conditions to include dust, moisture, or other corrosive explosives or foreign matter. These environmental conditions tend to have a harmful effect on the electrical switching and over a period of time could lead to switch malfunctions causing erronous indicator and control signals.
The prior art also includes U.S. Pat. No. 4,214,133. The applicant of the present invention was co-inventor of the subject matter disclosed and claimed in that patent. U.S. Pat. No. 4,214,133 solved the problems that were associated with the other prior art devices by providing a rotary shaft position indicator and control in which the electrical switch gear is enclosed within a housing that is sealed against the introduction of adverse matter. Switches are activated by a magnetic coupling through a wall of the housing. In one embodiment, the electrical switching is accomplished by a plurality of microswitches actuated by rotatably driven cams. The cams are driven by a magnetic coupling between two disks or annular magnets, one of the magnets being disposed outside of the housing. In an alternative embodiment, the microswitches are actuated by spring biased switch actuating arms on which were mounted bar-type magnets. A plurality of driving bar magnets are disposed outside of the housing in proximity to the housing wall to actuate an associated microswitch within the housing.
While the switch disclosed in U.S. Pat. No. 4,214,133 provided a sealed switch cavity it can be seen that the switch and switch actuating structure requires many mechanical components. The present device provides for less complex structure by utilizing magnetically actuated reed switches. These are particularly desirable in low voltage and low current applications. The present invention combines the advantages of the structure disclosed in U.S. Pat. No. 4,214,133 with the advantages of reed switch actuation.